If a large number of data packets is directed from an external network to users in an internal communication network, the internal network can become overloaded. This problem will be explained using the Internet as an example of an external network that is capable of sending an excessive number of data packets that can seriously hinder the operation of an internal network such as a radio data network or a paging network.
Users of the Internet are now able to send messages to individual radio receivers that operate in a radio network. The message starts at an Internet source, and is transmitted in the form of data packets to a radio network. The radio network transmits the received data packets to the addressee's radio receiver.
If an Internet source sends an excessive number of data packets to receivers in the radio network, the outbound channels of the radio network can become congested, and large bills can be run up for the addressed radio receivers. Such an attack on the radio network can be purposeful or inadvertent, such as by a sender of junk mail. In either event, the result is degraded service in the radio network, and large bills that are unlikely to be paid by unhappy recipients of the data packets.
A firewall between the Internet and the radio network is the traditional mechanism for protecting the radio network from an assault of the type described above. However, a conventional firewall also restricts arbitrary access by legitimate users. Moreover, some forms of such an attack, such as junk e-mail, can be successful, even through a firewall. Conventional packet filtering may protect the network, but it also can restrict access by legitimate users. Similar problems arise with other forms of external networks which are capable of sending large numbers of data packets to users in an internal network.